This invention deals generally with surface water purification, and more specifically with a catch basin which purifies surface water that flows through it.
As more land is being converted to commercial use, contamination of surface water is becoming more of a problem. Not only does the typical parking lot or street affect the natural flow of surface water, but it also significantly contaminates it. When walking through a typical parking lot or along a street it becomes apparent that such surfaces not only accumulate trash, but they also have numerous spills of oil and other fluids from automobiles and trucks. Furthermore, such contamination is not limited to parking lots used for commercial purposes. Parking lots for churches, schools and office buildings have the same problems.
Although it is well understood that all such construction must control its surface water runoff quantity, it is not fully appreciated that the poor quality of surface water coming off a typical parking lot can contaminate streams, estuaries, bays, and ground water supplies if the runoff from the vehicle parking lot is permitted to simply flow onto and sink into the ground.
Considerably more attention and regulation has been devoted to the purification of sewage water, referred to as point source pollution, than to the purification of surface runoff from parking lots and other impervious surfaces. However, the EPA has an effort underway for preventing and regulating such non-point source pollution sources.
It would be very beneficial to have a device which requires no outside power to purify parking lot and street runoff before it is added to streams and the groundwater supply.
The present invention is a self contained surface water purification unit which requires no outside power because the surface water flows through it under its own gravity induced power. The entire unit is built into a conventional appearing catch basin, usually a concrete vault in the shape of a rectangular prism. The catch basin is built with essentially two chambers, each serving a particular function.
The first chamber is the inlet chamber, and surface water enters into it high on an outside wall. The exit from the inlet chamber is located above the bottom, typically about one third of the way up a wall which separates the inlet chamber from the second chamber, the settling chamber.
The inlet chamber serves as both a floatation chamber and a settling basin. Contaminants which are heavier than water, including stones, metal, and gravel, sink to the bottom of the inlet chamber, while oil and other floating debris float to the top of the water, well above the sediment that has settled to the bottom.
When the water level in the inlet chamber reaches above the exit of the inlet chamber which is located high enough above the bottom of the inlet chamber to permit a significant volume for accumulation of the large debris, the water begins flowing into the second chamber, the settling chamber. The exit of the inlet chamber is located where it will usually be between the floating debris and heavier debris in the bottom of the inlet chamber, thus taking advantage of the natural tendency to separate solids and liquids by density.
The settling chamber contains a lamella separator. Such lamella separators are constructed of multiple parallel plates oriented at an angle to the vertical, and they function to settle fine sediment out of liquid moving up through the separator. The lamella separator is positioned to occupy about one-half the volume of the upper portion of the settling chamber. Surface water entering the settling chamber from the inlet chamber flows directly into the lamella separator, and as the water rises in the settling chamber, since the part of the settling chamber other than the portion holding the lamella separator is closed off by a partition, the water must go through the separator to leave the catch basin. Water going into the separator enters low at one side near the edges of the parallel plates, and the water leaving the separator exits high on the opposite side near the other edges of the plates.
As the surface water rises through the lamella separator, the fine sediment settles out and falls through the spacing between the plates at the bottom of the separator to the bottom of the settling chamber where it accumulates. The outlet for the entire catch basin is located in the upper portion of the settling chamber so that the water goes through the lamella separator before reaching the exit of the catch basin.
One structural feature in the catch basin operates as an emergency overflow. An overflow partition within the inlet chamber, parallel to and spaced from the wall dividing the two chambers forms a third partial chamber. The overflow partition extends down from the top of the inlet chamber to close to the exit of the inlet chamber. However, the divider wall between the chambers does not actually reach the top of the catch basin. Thus, if the inlet chamber becomes full, the water spills over the divider wall and directly into the top portion of the settling chamber, and the excess water leaves the catch basin without going through the lamella separator, but can not pick up the material previously settled out. The location of the overflow partition close to the divider wall also prevents most of the floating debris in the inlet chamber from overflowing into the settling chamber, because only that small amount of the floating debris between the divider wall and the overflow partition has access to the overflow above the divider wall.
Nevertheless, to aid in the removal of the oil in any overflow, and also in the normal flow, an oil capturing xe2x80x9cblanketxe2x80x9d can also be located within the portion of the settling chamber from which the liquid exits the catch basin. This blanket is a layer made of a hydrophobic, oil absorbing material, and the liquid flows over it before exiting.
The only maintenance required for the catch basin of the invention is the cleaning out of the two chambers and the occasional replacement of the oil capturing blanket when it is used. Access holes are provided for this in the top of each chamber. Access to the floating material and the large debris in the inlet chamber is straightforward since a pipe lowered through the access hole in the top can easily reach the floating material and the debris settled to the bottom. However, in the settling chamber an access door is provided in the partition between the upper and lower portions. When the access door is opened, a pipe can be lowered all the way to the bottom to pump out the fine sediment. The oil capturing blanket is also accessible through the access hole above the settling chamber.
The catch basin of the invention thereby furnishes a device to remove trash, oil, and both large and fine sediment, and the only maintenance it requires is the occasional removal of the accumulated contaminants. Furthermore, the lamella separator of the invention reduces the horizontal area used for settling to 12 to 25 percent of the area used by previously available simple gravity or single angular plate separators.